Bob Perry

In TWA how close to the wind can a TP 52 sail effectively?

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1 hour ago, Bob Perry said:

How high can you point in a TP 52 in "normal" conditions, measured in True Wind Angle? Thanks.

 

TWA 43-44deg in light to 36-37deg in medium wind and flat water, to over 40deg in more wind and waves.

This is for Med Cup style boats

The boats that were designed for the transpac are probably not as close winded

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16 minutes ago, us7070 said:

 

TWA 43-44deg in light to 36-37deg in medium wind and flat water, to over 40deg in more wind and waves.

This is for Med Cup style boats

The boats that were designed for the transpac are probably not as close winded

Wow, I would overshoot the windward mark most of the time!

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Yup. But dont forget, this is at bs of over 9 knots.

Ye olde 12m, upwind at 8.2 (Australia II) would tack through 68, i.e. twa 34 degrees

IACC boats not much different, albeit with leeway close to zero.

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4 hours ago, Frogman56 said:

albeit with leeway close to zero.

Albeit with rudder angles close to 10° ?

 

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10 hours ago, Frogman56 said:

Yup. But dont forget, this is at bs of over 9 knots.

Ye olde 12m, upwind at 8.2 (Australia II) would tack through 68, i.e. twa 34 degrees

IACC boats not much different, albeit with leeway close to zero.

That it interesting because the sheeting angles on the TP52's appear to be much narrower than on the 12s or IACC boats.

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Two data points for discussion:

2nd Gen TP in flat water, 8 knots of breeze, TWA of about 40-42°, lead about 4.5° off center line with an amateur driver and trimmer.  7.8 knots boat speed.  Helm at 3°

Med Cup boats in mid-teens breeze of 14 knots, TWA of 36°-38°, Jib lead about 3.2° off centerline with a pro driver and trimmer.  9.1 knots boat speed. Helm 

3-degrees-of-seperation-768x432.jpg

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1 hour ago, Left Shift said:

Two data points for discussion:

2nd Gen TP in flat water, 8 knots of breeze, TWA of about 40-42°, lead about 4.5° off center line with an amateur driver and trimmer.  7.8 knots boat speed.  Helm at 3°

Med Cup boats in mid-teens breeze of 14 knots, TWA of 36°-38°, Jib lead about 3.2° off centerline with a pro driver and trimmer.  9.1 knots boat speed. Helm 

3-degrees-of-seperation-768x432.jpg

So is 22 the AWA?

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2 hours ago, SF Woody Sailor said:

That it interesting because the sheeting angles on the TP52's appear to be much narrower than on the 12s or IACC boats.

You gotta think vectors.  In general:

1) I very much doubt 12 metres got down to 34 degrees, maybe 36 or 37.  Instrument calibrations being what they are TWA is always a bit suspect, and especially so back in 12m days when the systems were a lot less sophisticated than they are now.

2) AWA is the limiting factor.  A soft sail (jib), no matter how expensive will struggle to produce lift much below around 21 degrees AWA - and that in flat water.  Plug that into a vector equation with boat speed, wind speed, current and leeway and you will get a minimum TWA value.  For TP52s I'd guess its around 36-37 degrees - and that pic seems to support that. I understand upwind TWA values for the AC75s are around 55 degrees, simply because they move so fast relative to wind speed.

3) TP52s do big numbers upwind relative to wind speed.  9.3 or 9.5.  At this speed relative to wind speed the apparent wind angle closes down rapidly and TWA is limited.  An old 12m went much slower relative to wind speed hence could probably manage tighter TWA values for similar AWA values.

4) In bumpy sea states other factors apply - you need to aim for a TWA that provides good drive over a range of AWA angles (say 23-27) as it's not possible to steer as precisely as in flat water.  Aiming for tight AWA values like 21-22 degrees means the sail will be at times operating at AWA below 20 degrees and drive drops off rapidly when that happens and you really don't need that when the boat is trying to climb up waves.  So bumpy sea generally means a few degrees lower, with sails more twisted.  More so for a light boat like a TP52 than a lead mine which has better momentum and isn't thrown about as much by waves.

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8 minutes ago, DickDastardly said:

You gotta think vectors.  In general:

 I understand upwind TWA values for the AC75s are around 55 degrees, simply because they move so fast relative to wind speed.

 

The only interesting thing about the monster foiling multihulls racing in SF Bay was that the vectors yielded completely non-intuitive results. For example, those of us who grew up sailing monohulls on the Bay go to great lengths to stay in relief from the adverse current. But the AC72's were the other way around. Going downwind they eventually learned to search out the worst current possible because the increased apparent wind speed from, say, two knots of adverse current increased their boat speed by four knots. 

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1 hour ago, SF Woody Sailor said:

So is 22 the AWA?

Yep.  Can't get a whole lot finer than that with soft sails.

TP52s hit kind of a magic spot for monohull design..  Remarkable upwind and also pretty remarkable off the wind.   They would likely embarrass a IACC boat around a course and demolish a 12 meter.

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25 minutes ago, DickDastardly said:

You gotta think vectors.  In general:

1) I very much doubt 12 metres got down to 34 degrees, maybe 36 or 37.  Instrument calibrations being what they are TWA is always a bit suspect, and especially so back in 12m days when the systems were a lot less sophisticated than they are now.

2) AWA is the limiting factor.  A soft sail (jib), no matter how expensive will struggle to produce lift much below around 21 degrees AWA - and that in flat water.  Plug that into a vector equation with boat speed, wind speed, current and leeway and you will get a minimum TWA value.  For TP52s I'd guess its around 36-37 degrees - and that pic seems to support that. I understand upwind TWA values for the AC75s are around 55 degrees, simply because they move so fast relative to wind speed.

3) TP52s do big numbers upwind relative to wind speed.  9.3 or 9.5.  At this speed relative to wind speed the apparent wind angle closes down rapidly and TWA is limited.  An old 12m went much slower relative to wind speed hence could probably manage tighter TWA values for similar AWA values.

4) In bumpy sea states other factors apply - you need to aim for a TWA that provides good drive over a range of AWA angles (say 23-27) as it's not possible to steer as precisely as in flat water.  Aiming for tight AWA values like 21-22 degrees means the sail will be at times operating at AWA below 20 degrees and drive drops off rapidly when that happens and you really don't need that when the boat is trying to climb up waves.  So bumpy sea generally means a few degrees lower, with sails more twisted.  More so for a light boat like a TP52 than a lead mine which has better momentum and isn't thrown about as much by waves.

The above is true, but there are drivers and then there are driver teams.  A TP52, driven up wind by a Bora Gulari, with Ken Read calling for 1° helm adjustments and some other rock star calling wave trains is a different world.  

(But, fuck, they are fun to drive!!!  Just do NOT try to do anything else.)

 

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1 hour ago, Left Shift said:

Yep.  Can't get a whole lot finer than that with soft sails.

TP52s hit kind of a magic spot for monohull design..  Remarkable upwind and also pretty remarkable off the wind.   They would likely embarrass a IACC boat around a course and demolish a 12 meter.

In fairness, that was not the point of the 12s or the IACC's. They were intended to provide good match racing which they did. A match race downwind is a lot more tactically interesting in non-planing symmetrical spin boats than in planing asym boats due to the smaller gybing angles and smaller speed differentials. The ultimate proof is the catamarans which are so boring to watch going upwind all the way around the course.

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13 hours ago, Fiji Bitter said:

Albeit with rudder angles close to 10° ?

 

Nope, rudder probably close to neutral!

Trim tab on trailing edge of keel -  at least on the 12m boats, not sure if the IACC's had them?

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20 hours ago, Bob Perry said:

How high can you point in a TP 52 in "normal" conditions, measured in True Wind Angle? Thanks.

 

Depends if it is on port tack

apparently

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I had this same question watching the videos. I noticed the on screen tracks showing tacking angles fairly close to 90 degrees. perhaps these were lighter air days but looking at those jibs made me imagine much smaller tacking angles than I saw on the screen. To be fair, they were only in high mode when they were trying to get up to the mark.

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7 hours ago, SF Woody Sailor said:

The only interesting thing about the monster foiling multihulls racing in SF Bay was that the vectors yielded completely non-intuitive results. For example, those of us who grew up sailing monohulls on the Bay go to great lengths to stay in relief from the adverse current. But the AC72's were the other way around. Going downwind they eventually learned to search out the worst current possible because the increased apparent wind speed from, say, two knots of adverse current increased their boat speed by four knots. 

Yeah I remember hearing that. Had to think about it a bit but it made sense eventually. 

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The 12s and the IACC designs both had trim tabs, and both therefore close to zero leeway, probably around one degree for foil wash separation.

Grant Simmer A II navigator widely reported as stating 'overlaid at 70 degree tacking angle'

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8 hours ago, SF Woody Sailor said:

The only interesting thing about the monster foiling multihulls racing in SF Bay was that the vectors yielded completely non-intuitive results. For example, those of us who grew up sailing monohulls on the Bay go to great lengths to stay in relief from the adverse current. But the AC72's were the other way around. Going downwind they eventually learned to search out the worst current possible because the increased apparent wind speed from, say, two knots of adverse current increased their boat speed by four knots. 

I would guess thats more an apparent boat speed thing.  Hulls out of the water, going against the tide gives you more flow over the foils

Flood always gives you less AWS, ebb always gives more. 

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9 minutes ago, some dude said:

I would guess thats more an apparent boat speed thing.  Hulls out of the water, going against the tide gives you more flow over the foils

Flood always gives you less AWS, ebb always gives more. 

Umm, apparent boat speed? Might want to put down that morning rum for a minute.

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23 minutes ago, SF Woody Sailor said:

Umm, apparent boat speed? Might want to put down that morning rum for a minute.

Yep.  There's this thing in SF Bay called current.  Foiling boat moves through the air at, say, 30.  5 knots flood as it goes upwind, 35 knots over the foils.  Downwind, 25 knots over the foils.  

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2 minutes ago, some dude said:

Yep.  There's this thing in SF Bay called current.  Foiling boat moves through the air at, say, 30.  5 knots flood as it goes upwind, 35 knots over the foils.  Downwind, 25 knots over the foils.  

Boat speed is speed through the water. There is no such thing as "apparent boat speed" as distinguished from boat speed. Boat speed is the same whether you are on a displacement boat, a planing boat or a foiling boat. You can get boat speed from an impeller or ultrasonic sensor, or from throwing woodchips off the bow with a stopwatch if you are old school. Speed Over Ground (SOG) is the combination of the vector of boat speed, heading, and current set and drift. You can work this out with graph paper if it helps. Your GPS can display SOG and COG, and your instruments can calculate current set and drift from SOG, COG, boatspeed and heading.

Apparent wind angle and velocity are more complicated. It is the vector combination of boat speed, true wind speed, true wind angle, current set and drift and leeway. Fortunately, instruments can display the apparent numbers easily.

Calculating true wind speed and true wind angle from the apparent numbers is much more complicated, and very few instruments are calibrated well enough to do this accurately. 

 

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11 minutes ago, SF Woody Sailor said:

Boat speed is speed through the water. There is no such thing as "apparent boat speed" as distinguished from boat speed. Boat speed is the same whether you are on a displacement boat, a planing boat or a foiling boat. You can get boat speed from an impeller or ultrasonic sensor, or from throwing woodchips off the bow with a stopwatch if you are old school. Speed Over Ground (SOG) is the combination of the vector of boat speed, heading, and current set and drift. You can work this out with graph paper if it helps. Your GPS can display SOG and COG, and your instruments can calculate current set and drift from SOG, COG, boatspeed and heading.

Apparent wind angle and velocity are more complicated. It is the vector combination of boat speed, true wind speed, true wind angle, current set and drift and leeway. Fortunately, instruments can display the apparent numbers easily.

Calculating true wind speed and true wind angle from the apparent numbers is much more complicated, and very few instruments are calibrated well enough to do this accurately. 

 

Yep very similar concept for boats sailing with the hull in the water (which is most of us of course)  Now you're catching on. 

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1 minute ago, some dude said:

Yep very similar concept for boats sailing with the hull in the water (which is most of us of course)  Now you're catching on. 

That wooshing sound was the point going over your head.

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27 minutes ago, SF Woody Sailor said:

That wooshing sound was the point going over your head.

Messed up my hairdo 

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On 8/9/2020 at 6:42 AM, us7070 said:

 

TWA 43-44deg in light to 36-37deg in medium wind and flat water, to over 40deg in more wind and waves.

This is for Med Cup style boats

The boats that were designed for the transpac are probably not as close winded

Wow. The old 1992 RP 50 I sail the targets are: 45-46 degrees TWA, 21-22 AWA. Flat water, 9-12 knots. Pretty good for a 28 year old boat. 

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19 minutes ago, no shoes said:

Wow. The old 1992 RP 50 I sail the targets are: 45-46 degrees TWA, 21-22 AWA. Flat water, 9-12 knots. Pretty good for a 28 year old boat. 

See post #10.

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Post #22:  Current does not affect speed through the water (i.e. boat speed).  It does affect the speed over ground, thus it affects the apparent wind.  The AC cats are so responsive to wind velocity that the increase in pressure from sailing in "anti-water" increased the boat speed more than the loss of SOG.

Post #23:  Apparent wind angle is a first level bit of data, as is boat speed.  Pulled straight off the instrument data and displayed or integrated.  It is conversion of AWA into true wind angle that is difficult.  Any second or third generation calculated data (e.g. True Wind Angle) that is not coming out of an AC or Med Cup campaign, where they have factory instrument guys calibrating the sensors and computer nerds on shore tracking and verifying the data  is highly suspect.  Or put more bluntly, very likely to be inaccurate, quite possibly to the point of being useless.  

 

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14 minutes ago, Left Shift said:

Post #22:  Current does not affect speed through the water (i.e. boat speed).  It does affect the speed over ground, thus it affects the apparent wind.  The AC cats are so responsive to wind velocity that the increase in pressure from sailing in "anti-water" increased the boat speed more than the loss of SOG.

Post #23:  Apparent wind angle is a first level bit of data, as is boat speed.  Pulled straight off the instrument data and displayed or integrated.  It is conversion of AWA into true wind angle that is difficult.  Any second or third generation calculated data (e.g. True Wind Angle) that is not coming out of an AC or Med Cup campaign, where they have factory instrument guys calibrating the sensors and computer nerds on shore tracking and verifying the data  is highly suspect.  Or put more bluntly, very likely to be inaccurate, quite possibly to the point of being useless.  

 

Thanks for repeating exactly what I said!

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4 minutes ago, SF Woody Sailor said:

Thanks for repeating exactly what I said!

You certainly have the right idea, but I think you may have inadvertently just flipped the AWA and TWA terms in your post.  "Apparent wind angle and velocity are more complicated. It is the vector combination of boat speed, true wind speed, true wind angle, current set and drift and leeway. Fortunately, instruments can display the apparent numbers easily."   

I agree that TWA and TWS can be displayed quite easily.  Getting them to be accurate is the trick.  I rarely believe the displayed TWA and TWS data, certainly not enough to steer by.  

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23 minutes ago, Left Shift said:

Pulled straight off the instrument data and displayed or integrated.  It is conversion of AWA into true wind angle that is difficult.  Any second or third generation calculated data (e.g. True Wind Angle) that is not coming out of an AC or Med Cup campaign, where they have factory instrument guys calibrating the sensors and computer nerds on shore tracking and verifying the data  is highly suspect.  Or put more bluntly, very likely to be inaccurate, quite possibly to the point of being useless.   

It is easy to check though. At the windward or the leeward mark you check if the wind direction and/or wind speed suddenly changes as you round the mark. If not, instrument calibration is probably good enough for mere mortals.

 

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7 minutes ago, Left Shift said:

You certainly have the right idea, but I think you may have inadvertently just flipped the AWA and TWA terms in your post.  "Apparent wind angle and velocity are more complicated. It is the vector combination of boat speed, true wind speed, true wind angle, current set and drift and leeway. Fortunately, instruments can display the apparent numbers easily."   

I agree that TWA and TWS can be displayed quite easily.  Getting them to be accurate is the trick.  I rarely believe the displayed TWA and TWS data, certainly not enough to steer by.  

I said "instruments can display the apparent numbers easily."   "Calculating true wind speed and true wind angle from the apparent numbers is much more complicated, and very few instruments are calibrated well enough to do this accurately"

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6 minutes ago, Panoramix said:

It is easy to check though. At the windward or the leeward mark you check if the wind direction and/or wind speed suddenly changes as you round the mark. If not, instrument calibration is probably good enough for mere mortals.

 

A real litmus test is light air gybes. Almost no instrument system that is not professionally and continually calibrated will read the same true wind angle before and after a light air, reach to reach gybe.

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15 minutes ago, Left Shift said:

I rarely believe the displayed TWA and TWS data, certainly not enough to steer by.  

Who tries to steer by true numbers? I don't think even autopilots are that dumb. As a tactician I would hide the true numbers from the driver if I could. Boatspeed and apparent wind are generally enough for the helmsman and trimmers; sometimes wind speed can also be helpful to the trimmers. True numbers are only of interest to the tactician (and navigator/strategist if present).

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4 hours ago, SF Woody Sailor said:

Who tries to steer by true numbers? I don't think even autopilots are that dumb. As a tactician I would hide the true numbers from the driver if I could. Boatspeed and apparent wind are generally enough for the helmsman and trimmers; sometimes wind speed can also be helpful to the trimmers. True numbers are only of interest to the tactician (and navigator/strategist if present).

Concur completely. 

However, I had a boat partner who tried, insisted on it actually.  Didn't last long as a partner.  That may the cause of my heightened sensitivity on this issue.  It may also be the reason I'm bald.

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4 hours ago, SF Woody Sailor said:

Who tries to steer by true numbers? I don't think even autopilots are that dumb. As a tactician I would hide the true numbers from the driver if I could. Boatspeed and apparent wind are generally enough for the helmsman and trimmers; sometimes wind speed can also be helpful to the trimmers. True numbers are only of interest to the tactician (and navigator/strategist if present).

This is a common misunderstanding, but if you are running the B&G H5000 system, the AWA and AWS are actually back calculated by the computer, based on its calculated TWS and TWA values

With H5000, there is no real raw unprocessed AWA, the closest is a “red phase”, “green phase”, and “blue phase”, which measures voltage on three wires.  If you have the H5000, you calibrate the whole system, and your If your AWA is accurate, so will your TWA. But no one is going to be steering to “1.3v on red phase”

 

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Can't be bothered to read up posts.  On the boat I currently sail with, (H5 system), I have target TWA and BS displayed on the bottom display of the mast.  TWA is displayed higher up and is consistently referred to by any of the helm and trimmers upwind and downwind. Upper image is target TWA, lower is target BS.

As an aside, in the older days downwind sailing with symetricals or even aysos poled back, I would much rather sail to TWA on a pitch black night surfing downwind than to sail to AWA.

image1.png

image0.png

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27 minutes ago, Salona said:

This is a common misunderstanding, but if you are running the B&G H5000 system, the AWA and AWS are actually back calculated by the computer, based on its calculated TWS and TWA values

With H5000, there is no real raw unprocessed AWA, the closest is a “red phase”, “green phase”, and “blue phase”, which measures voltage on three wires.  If you have the H5000, you calibrate the whole system, and your If your AWA is accurate, so will your TWA. But no one is going to be steering to “1.3v on red phase”

 

 

11 minutes ago, Hitchhiker said:

Can't be bothered to read up posts.  On the boat I currently sail with, (H5 system), I have target TWA and BS displayed on the bottom display of the mast.  TWA is displayed higher up and is consistently referred to by any of the helm and trimmers upwind and downwind. Upper image is target TWA, lower is target BS.

As an aside, in the older days downwind sailing with symetricals or even aysos poled back, I would much rather sail to TWA on a pitch black night surfing downwind than to sail to AWA.

image1.png

image0.png

Ah, the olden days...when you pushed as deep as you could go without scaring the shit out the crew when the main floated into the centerline on a surf and you weren't quite sure which side it would decide to refill on because the compass was wandering around and the TWA wasn't updating very fast. 

The windex is your friend.

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10 minutes ago, Left Shift said:

 

 

The windex is your friend.

Not at 20 plus knots of speed when it's mounted 50 plus feet in the air!

Not saying I would remove it, but not much chance to look at it.

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9 hours ago, SF Woody Sailor said:

Who tries to steer by true numbers? I don't think even autopilots are that dumb. As a tactician I would hide the true numbers from the driver if I could. Boatspeed and apparent wind are generally enough for the helmsman and trimmers; sometimes wind speed can also be helpful to the trimmers. True numbers are only of interest to the tactician (and navigator/strategist if present).

+1 on that, though the TWA/TWS values on modern high-end systems are pretty good these days but as mentioned above - a lot of effort is required to get them that good and indeed keep them there.

At a club level, using Expedition or something similar to log your race data provides a lot of useful input to calibration given that investing crew days on the water in instrument calibration is normally not easy to do.  Top-end programs often pay rail meat and one or two pros to take the boat out for dedicated calibration days - but even then getting data across a wide range of wind and sea states is hard.

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5 hours ago, Salona said:

This is a common misunderstanding, but if you are running the B&G H5000 system, the AWA and AWS are actually back calculated by the computer, based on its calculated TWS and TWA values

With H5000, there is no real raw unprocessed AWA, the closest is a “red phase”, “green phase”, and “blue phase”, which measures voltage on three wires.  If you have the H5000, you calibrate the whole system, and your If your AWA is accurate, so will your TWA. But no one is going to be steering to “1.3v on red phase”

 

There are actually MWA and MWS Variables in H5000 systems though strangely only available over the Websocket interface.  These are the raw (undamped and uncalibrated) AWA and AWS values form the masthead.  It's useful to log these against AWA and AWS to give an overview of how your calibrations are working.

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4 hours ago, Hitchhiker said:

image1.png

 

image0.png

Sorry but my boomer eyes can not make out any details of those microscope photos. I think the person on the left of the bottom photo is male but these days, who can tell?

 

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57 minutes ago, Somebody Else said:

Sorry but my boomer eyes can not make out any details of those microscope photos. I think the person on the left of the bottom photo is male but these days, who can tell?

 

Too bad.  It won't get any easier to read the fine print or figure out gender in a non gender specific society.

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7 hours ago, Salona said:

This is a common misunderstanding, but if you are running the B&G H5000 system, the AWA and AWS are actually back calculated by the computer, based on its calculated TWS and TWA values

With H5000, there is no real raw unprocessed AWA, the closest is a “red phase”, “green phase”, and “blue phase”, which measures voltage on three wires.  If you have the H5000, you calibrate the whole system, and your If your AWA is accurate, so will your TWA. But no one is going to be steering to “1.3v on red phase”

 

Why do they do this? It is silly, if one measured value is wrong you lose everything.

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13 hours ago, SF Woody Sailor said:

Who tries to steer by true numbers? I don't think even autopilots are that dumb. 

It's reasonably common short-handed to set the pilot to steer to AWA upwind, HDG on a reach and TWA downwind. IIRC in the B&G H5000 pilot in vane mode you can set a threshold TWA where it switches automatically.

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14 hours ago, SF Woody Sailor said:

Who tries to steer by true numbers? I don't think even autopilots are that dumb. As a tactician I would hide the true numbers from the driver if I could. Boatspeed and apparent wind are generally enough for the helmsman and trimmers; sometimes wind speed can also be helpful to the trimmers. True numbers are only of interest to the tactician (and navigator/strategist if present).

It has occurred to me many times that apparent wind is the thing our sails feel and respond to, and that TWA/TWS are calculated and therefore subject to error. What seems incongruous therefore is why polars are expressed in TWA. I have a set of polars that have both TWA and AWA on them but we end up using the TWA anyway but this has reminded me to think more about it. 

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38 minutes ago, danstanford said:

It has occurred to me many times that apparent wind is the thing our sails feel and respond to, and that TWA/TWS are calculated and therefore subject to error.

With the B&G H5000, pretty much all the values are calculated and need to be frequently calibrated to be reliable. While the boat does “feel” AWA, what’s displayed on your instrument is still based on the same trigonometry used to show TWA and will only be right if you took the time to set up the heal/bspd/leeway/etc compensation tables.

38 minutes ago, danstanford said:

I have a set of polars that have both TWA and AWA on them but we end up using the TWA anyway but this has reminded me to think more about it.

The best reason to use TWA is to more easily decide on sails and course selection at the next mark, because the navigator can easily convert between TWA, heading, and true wind direction. Because AWA changes based on boat speed, it can’t really be used for that tactic or nav decisions.

The other strike against Using AWA for targets is that  can easily end up driving in a big semi circle as you “chase” the AWA accelerating down waves etc. The problem is magnified at night or downwind. You can use dampening to compensate for this... but then why not just use TWA?

But if you want the most responsive and generally unprocessed number to steer to, use boat speed as the target.  Though it will still be a dampened value and is affected by waves, heel angle, etc...

 

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39 minutes ago, danstanford said:

What seems incongruous therefore is why polars are expressed in TWA

It would be somewhat tricky to do a weather routeing with AWA polars. Also your measured AWA is still dirty because of heel, upwash, shear, leeway and so on.

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38 minutes ago, danstanford said:

It has occurred to me many times that apparent wind is the thing our sails feel and respond to, and that TWA/TWS are calculated and therefore subject to error. What seems incongruous therefore is why polars are expressed in TWA. I have a set of polars that have both TWA and AWA on them but we end up using the TWA anyway but this has reminded me to think more about it. 

TWA is much more convenient at the the chart table. wind is 300my heading is O, so TWA is 60 on port then you can directly read your surface speed from the polar. Actually only if the current speed is small enough to be negligible which is obviously not always true.

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This is turning into the most informative thread drift I've seen in a while.

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45 minutes ago, V21 said:

This is turning into the most informative thread drift I've seen in a while.

Yea,  we still don't know what Mr. Perry is up to, .... Roberto, whatcha doing?  Rick

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20 hours ago, SF Woody Sailor said:

Who tries to steer by true numbers? I don't think even autopilots are that dumb. As a tactician I would hide the true numbers from the driver if I could. Boatspeed and apparent wind are generally enough for the helmsman and trimmers; sometimes wind speed can also be helpful to the trimmers. True numbers are only of interest to the tactician (and navigator/strategist if present).

I wish that were the case but there's a reason performance boats pay extra to unlock the TWA feature their autopilots.  While I've never seen an autopilot steer a performance boat well to AWA, on TWA the sensors for pitch and roll seem to override the TWA command to keep boats planing and adjusting for waves, especially off the wind, sort of simulating how we steer.  Buy an off the shelf pilot from West Marine and set it to AWA and you will be going back to compass steering in no time, with TWA N/A.

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5 hours ago, Salona said:

The other strike against Using AWA for targets is that  can easily end up driving in a big semi circle as you “chase” the AWA accelerating down waves etc. The problem is magnified at night or downwind. You can use dampening to compensate for this... but then why not just use TWA?

Yup - full dark no horizon surfing.  On the bright side, watching and waiting for the newbie offshore driver to drop into a surf and slowly turn the boat into a crash gybe by chasing AWA does keep you awake.  Damping helps some but getting them to use TWA and average compass headings reduces the number of scary bottom turns and wheel grabs.     

 

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The most efficient apparent wind angle is built into the boat's aero and hydrodynamics and is pretty much fixed (it is the sum of the drag angles of water and wind). The TWA then depends on boat speed, and there is a boat speed at which VMG is maximized. Going faster than that actually reduces VMG. After listening to too many catamaran salesmen tell me, "well, they do point a little lower but you make it up with boat speed" I did the spreadsheet. Here is the curve for a boat that sails most efficiently at 29 AWA, in 10 knots pressure. Note that the VMG peaks at about 10 knots BS. Going faster will get you there slower because the TWA decays. To go fast to windward, a fast boat must also be extraordinarily weatherly as it suffers more from TWA shift. 

KAqLttK.jpg

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Here's an easy solution that doesn't rely on fancy instruments requiring calibration - put a GPS waypoint on your windward mark, set the GPS to "goto waypoint", then watch the VMG towards the waypoint change as you sail a few degrees higher or a few degrees lower.   

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9 hours ago, Panoramix said:

Why do they do this? It is silly, if one measured value is wrong you lose everything.

The expression that derives TWA from AWA etc. is entirely reversible. It could give the identical result. One can assume there is a good reason for what they do. Perhaps filtering, calibrating and compensation is more effective in the True space than in the Apparent space.

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A lot of this discussion is about autopilots which is great shorthanded or offshore, but for those of us who do fully crewed buoy racing that topic not very relevant.

I like to give my helmsman AWA and boatspeed. Magnetic Heading is also useful as a rough guide whether he is in a header or lift so he doesn't get lost in the numbers (although a good helmsman shouldn't). Target boatspeed can be helpful upwind as long as it is dampened and reasonably accurate. It is misleading on any other point of sail.

The trimmers can use also wind speed to get to their correct settings for the current conditions (including sea state) and for input on next leg sail selection.

In my view all of the true (calculated) numbers such as TWA, TWD, TWS, VMG, current set and drift, leeway, etc. should be available to the tactician and navigator and hidden from the helmsman and trimmers. There is no reason they need to know, and surplus information distracts them from the task at hand.

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TWA and an accurate set of polars are great and if you can steer that accurately, you'll do well.

Hard to do. Better for the nav/tact to figure it out and give the helmsman something easier like AWA to steer for.

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Two TP-52 Polar from ORCi  2020 VPP

The you can say from 44 to 36 may be slightly better as the TP-52 rates well.

The upper is a 1st Generation of 2008 and the down below is second generation of 2012

TP-52 1st Gen.png

TP-52 2nd Gen.png

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16 minutes ago, Somebody Else said:

TWA and an accurate set of polars are great and if you can steer that accurately, you'll do well.

Hard to do. Better for the nav/tact to figure it out and give the helmsman something easier like AWA to steer for.

My view:

Upwind give the driver target boat speed, instructions for high/low mode and allow an occasional glance at the compass.  Get the trimmers setting up the boat for the conditions.  Keep AWA out of it.

Downwind, use apparent wind angle and target boat speed with instructions to push deep or press for speed.  Even though it may be 70' up in the air, the windex is still the best tool for AWA.

Ocean waves, Set the boat up for balance and about 20° course tolerance, let the driver have fun using compass and AWA/windex to stay out of the deep shit.  

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2 minutes ago, storosis said:

 

TP-52 2nd Gen.png

Worth taking a moment to read this table and reflect on how fucking fast these machines are (or how broken the VPP is, depending on your perspective). 5 kts VMG up in 6 kts TWS is just obscene for a non-foiling monohull.  

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2 minutes ago, Snowden said:

Worth taking a moment to read this table and reflect on how fucking fast these machines are (or how broken the VPP is, depending on your perspective). 5 kts VMG up in 6 kts TWS is just obscene for a non-foiling monohull.  

It's not broken the most of TP-52 rates fairly well under ORCi

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4 hours ago, gspot said:

Here's an easy solution that doesn't rely on fancy instruments requiring calibration - put a GPS waypoint on your windward mark, set the GPS to "goto waypoint", then watch the VMG towards the waypoint change as you sail a few degrees higher or a few degrees lower.   

As long as this is allowed its the best and simplest way to do it. However, in many smaller classes it isn’t. Read your SI ! 

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4 hours ago, gspot said:

Here's an easy solution that doesn't rely on fancy instruments requiring calibration - put a GPS waypoint on your windward mark, set the GPS to "goto waypoint", then watch the VMG towards the waypoint change as you sail a few degrees higher or a few degrees lower.   

No offense but we must be talking about different things. I think most of us are talking about keelboats large and competitive enough to have instruments. "A few degrees" one way or the other is light years. This is not like strategic nuclear warfare where "pretty close" is a good result.

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4 hours ago, DDW said:

The most efficient apparent wind angle is built into the boat's aero and hydrodynamics and is pretty much fixed (it is the sum of the drag angles of water and wind). The TWA then depends on boat speed, and there is a boat speed at which VMG is maximized. Going faster than that actually reduces VMG. After listening to too many catamaran salesmen tell me, "well, they do point a little lower but you make it up with boat speed" I did the spreadsheet. Here is the curve for a boat that sails most efficiently at 29 AWA, in 10 knots pressure. Note that the VMG peaks at about 10 knots BS. Going faster will get you there slower because the TWA decays. To go fast to windward, a fast boat must also be extraordinarily weatherly as it suffers more from TWA shift. 

KAqLttK.jpg

 

30 minutes ago, 10thTonner said:

As long as this is allowed its the best and simplest way to do it. However, in many smaller classes it isn’t. Read your SI ! 

 

20 minutes ago, SF Woody Sailor said:

No offense but we must be talking about different things. I think most of us are talking about keelboats large and competitive enough to have instruments. "A few degrees" one way or the other is light years. This is not like strategic nuclear warfare where "pretty close" is a good result.

My point was to use this technique (e.g. during practice) to establish your own set of speed targets to optimize VMG for given conditions and points of sail  in case you don’t already have them.

i get that people on the pointy end of TP52 competitiveness probably won’t do this,  but they also won’t likely be looking for advice on an SA forum like this.

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2 hours ago, storosis said:

Two TP-52 Polar from ORCi  2020 VPP

The you can say from 44 to 36 may be slightly better as the TP-52 rates well.

The upper is a 1st Generation of 2008 and the down below is second generation of 2012

TP-52 1st Gen.png

TP-52 2nd Gen.png

The difference may be the introduction of fathead mains as class standard.  

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4 hours ago, Left Shift said:

My view:

Upwind give the driver target boat speed, instructions for high/low mode and allow an occasional glance at the compass.  Get the trimmers setting up the boat for the conditions.  Keep AWA out of it.

Downwind, use apparent wind angle and target boat speed with instructions to push deep or press for speed.  Even though it may be 70' up in the air, the windex is still the best tool for AWA.

Ocean waves, Set the boat up for balance and about 20° course tolerance, let the driver have fun using compass and AWA/windex to stay out of the deep shit.  

I'd second that upwind, downwind I use Target Boatspeed and TWA.  Often display TWA Delta on the instruments - as in the difference between TWA and Target TWA.  Helpful to inform helmsman that they are on target speed but x degrees above or ideally below Target TWA

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You nerds are killing me. From here on out, I’m setting all displays to sea temp and steering to that. 

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1. Put up the correct sails for the wind, course axis and sea state

2. Know what the target heel angle is; i.e. use the correct amount of RM, usually near 100% in tp

3. Get the twa right and you should be at targets +/- 0.3

4. Heel angle, heel angle, heel angle

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1 hour ago, Monkey said:

You nerds are killing me. From here on out, I’m setting all displays to sea temp and steering to that. 

Works for the Bermuda Race, anyway.

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1 hour ago, DickDastardly said:

I'd second that upwind, downwind I use Target Boatspeed and TWA.  Often display TWA Delta on the instruments - as in the difference between TWA and Target TWA.  Helpful to inform helmsman that they are on target speed but x degrees above or ideally below Target TWA

That's what the crew on the rail is for!  

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11 minutes ago, Left Shift said:

That's what the crew on the rail is for!  

What every helmsman secretly wants is steering input from everyone on the rail. ^_^

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Actually it's the comments like "We should have tacked 5 minutes ago" and "They are gaining on us" that drivers and tacticians really long for.  I'll take "You're high!" any day.

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11 minutes ago, Left Shift said:

Actually it's the comments like "We should have tacked 5 minutes ago" and "They are gaining on us" that drivers and tacticians really long for.  I'll take "You're high!" any day.

"We are overstood" is a personal favorite although "you are ranging negative" is a close second. Bonus points if two different crew members say both simultaneously. 

I am also a fan when one crew on the rail says "more pressure coming" while another says "chop ahead"

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1 hour ago, Left Shift said:

Works for the Bermuda Race, anyway.

I was trying to be a smart ass. Please don’t encourage my stupidity. 

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On 8/9/2020 at 10:28 PM, Bob Perry said:

How high can you point in a TP 52 in "normal" conditions, measured in True Wind Angle? Thanks.

 

I think everyone here has missed a critical question.   What are you building? 

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2 hours ago, SF Woody Sailor said:

"We are overstood" is a personal favorite although "you are ranging negative" is a close second.

I’m ranging negative? Sounds like I need another beer then, cobber!

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6 hours ago, SF Woody Sailor said:

What every helmsman secretly wants is steering input from everyone on the rail. ^_^

Gold

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3 hours ago, Spoonie said:

I think everyone here has missed a critical question.   What are you building? 

Don't use the North Queensland polars, don't seem very fast today.

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23 hours ago, 10thTonner said:

As long as this is allowed its the best and simplest way to do it. However, in many smaller classes it isn’t. Read your SI ! 

What? Where is this not allowed?

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22 hours ago, SF Woody Sailor said:

What every helmsman secretly wants is steering input from everyone on the rail. ^_^

I'm going platinum on this one

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The thing to remember about boats like the TP52 is that they have narrow sheeting angles because they can point.  Not that they point because they have narrow sheeting angles.  They are light and have very straight lines when heeled, and have a very efficient pair of low wetted surface airfoils under water, so they don't need a ton of power.  But they have a ton of power, and are de-powering anytime the breeze is over 12 true.  So you can burn the power by sheeting in as much as twisting off.  

Best advice I ever had about driving a boat with a set of foils like the TP is to settle in, find the right heel angle, build speed then wait for the moment when you can "fly the foils".  Lightly lean on them and go uphill.  

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